A 13-year-old cryptorchid Yorkshire terrier dog was referred because of a recurrent abdomen-filling mass. One year before referral, an abdominal mass was surgically removed and revealed to contain 2 testes with seminoma and rudimentary uterine tissue attached to it. At the time of referral, an abdominal mass had recurred; computed tomographic and histopathologic assessments of Tru-Cut (Merit Medical) biopsies revealed that the mass was lymph node metastasis of seminoma. Palliative-intent, intensity-modulated radiation therapy was delivered at the start as 15.2 Gy in 4 fractions over 2 consecutive days, and 4 wk later with 7.6 Gy in 2 fractions on the same day. Gross tumor volume reduced from 343.3 to 42.4 cm3 in 4 wk. The 15.2 Gy protocol was repeated after 6 mo, with further tumor size reduction to 29.3 cm3. Mild, small-intestinal diarrhea and decreased appetite were only noticed after the first radiation therapy and were self-limiting within 2 wk. To the best of the authors' knowledge, this is the first reported use of successful radiation therapy with a short-period protocol in a Yorkshire terrier with abdominal seminoma and persistent Müllerian duct syndrome. Key clinical message: A short-period radiation protocol was effective for the treatment of abdominal metastasized seminoma in a dog.